The present invention relates to the building and construction sector. More precisely, the invention relates to a concrete whose setting is initiated after it has been poured, and to a method for initiating the setting of said concrete.
The concrete currently in use in special works has a rheology which is not adapted to the criteria for the preparation of deep foundations.
The major problem is the change in the rheology. In fact, the initial set time is very often shorter than the concreting time; this results in the production of structures in which the following are observed:
poor coating of the reinforcements,
inclusions of drilling sludge,
poor adhesion between the concrete and the reinforcements.
Attempts to modify these concretes with adjuvants do not easily make it possible, if at all, to attain the desired rheology, thereby limiting the volume of concrete pours and hence the efficiency.
The invention proposes to overcome these disadvantages by means of a concrete whose setting is initiated after it has been poured. Said concrete will hereafter be called xe2x80x9cdelayed-setting concretexe2x80x9d.
Thus, according to a first feature, the invention relates to a delayed-setting concrete based on blast furnace slag.
Said concrete advantageously consists of a mixture essentially comprising a blast furnace slag, aggregates such as sand and/or coarse or fine gravels, and water.
The blast furnace slag generally represents from about 10% to about 35% by weight of the concrete composition. Although the nature of the blast furnace slag is not particularly critical, it is preferably of the basic type and the weight ratio CaO/SiO2 is preferably between about 1.10 and about 1.35. As an example of slag which can be used within the framework of the present invention, there may be mentioned a material comprising the following main components (in percentages by weight): 33 to 40% of SiO2, 8 to 16% of Al2O3, 39 to 44% of CaO, 4 to 9% of MgO and 0.5 to 1.5% of a source of S2xe2x88x92 ions.
The customary aggregates used to make concrete, namely sand and/or coarse or fine gravels, generally represent from about 60% to about 80% by weight of the concrete composition, the remainder of the mixture consisting of water.
The concrete according to the invention can also comprise any inert material commonly used in this field, for example fly ash and/or calcareous or siliceous fillers. In this case the amount of inert materials used is between about 5% and about 30% by weight, based on the weight of the blast furnace slag.
According to the invention, the blast furnace slag advantageously has a grain size below about 200 xcexcm, preferably below about 100 xcexcm. It is desirable that this grain size should not be below about 30 xcexcm.
The concrete according to the invention does not set as such. It therefore enables indefinite volumes to be concreted without the risk of defects induced by premature initial setting.
According to the invention, the setting of the concrete is initiated after it has been poured into the trenches.
Thus, according to another feature, the invention relates to a method of initiating the setting of the concrete described above, which consists in activating the blast furnace slag.